Conventionally, as the joints including knee sections, there have been known a single-axis knee joint that is a joint including a knee section with a single axis, and a multi-articulated link knee joint that is a joint including a knee section of a multi-articulated link mechanism.
A multi-articulated link knee joint includes various advantages as compared with a single-axis joint.
For example, in a multi-articulated link knee joint, the position of the instantaneous center of rotation of a knee section is in the position closer to a hip joint as compared with a single-axis knee joint, and therefore, the multi-articulated link knee joint includes the advantage of hardly dropping off at an early stage of standing as compared with the single-axis joint.
Further, in the multi-articulated link knee joint, the lower leg length becomes shorter at the time of bending of the knee section as compared with a single-axis knee joint, and therefore, the distance between the toe and the ground is large when the multi-articulated link knee joint is swung out by walking. Therefore, the multi-articulated link knee joint includes the advantage that the toe is hardly caught by the ground. By the advantage, the multi-articulated link knee joint can obtain beautiful gait without a vertical movement, as compared with a single-axis knee joint.
Further, a multi-articulated link knee joint includes the advantage that the knee cap hardly protrudes at the time of being in a sitting position as compared with a single-axis knee joint.
Further, a multi-articulated link knee joint includes the advantage that even when a user of an artificial leg with knee disarticulation or a long stump uses the multi-articulated link knee joint, the thigh length thereof can be made closer to the thigh length of a well leg, as compared with a single-axis knee joint.
Conventionally, as a multi-articulated link knee joint, there has been known a knee joint that includes a knee section of a multi-articulated link mechanism, an air cylinder that assists an action of the knee section, and a computer that controls an operation of the air cylinder (See Japanese laid-open patent publication No. 2000439974 A and Japanese laid-open patent publication No. 2004-167106 A, for example.).